fix: Snowflake - Stop asserting views start with SELECT (CTEs).

[DanCardin]

i believe that assert was more a guard against bugs in the code that processed the query, but taking into account WITH-starting queries, it just doesn't seem worth it to keep expanding the assert.

if there's some other definition structure that causes this to fail, we can address that more directly with better parsing.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.86%. Comparing base (545cd8e) to head (11c747d).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...declarative_extensions/dialects/snowflake/query.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #108      +/-   ##
==========================================
- Coverage   89.87%   89.86%   -0.01%     
==========================================
  Files          85       85              
  Lines        3811     3810       -1     
  Branches      778      778              
==========================================
- Hits         3425     3424       -1     
  Misses        314      314              
  Partials       72       72              

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